In a global radio telecommunications system, the system and those who operate the system generally have no control over where the subscriber units are located. The communication system though, is responsible for granting or denying particular communication services depending upon whether or not the system has received permission to operate at a location where a particular subscriber unit may happen to be located. Moreover, the system may be responsible for billing in connection with the use of communication services, and the rates charged for such services and parties to receive revenues from the services may vary from location to location.
A radio telecommunications system may grant and deny particular communication services and assign particular billing rates to calls if it knows the locations of the subscriber units. Accordingly, it would be desirable to configure the system so that the locations of subscriber units are determined and so that information describing locations is transmitted to controllers which are responsible for making decisions regarding the granting or denying of communication services, billing rates, and the like. Preferably, locations are determined as quickly as possible so that service interruptions are minimized.
Many prior art location determination systems are known, such as Global Positioning System (GPS), GLONASS, Loran, and the like. While subscriber units could be configured to incorporate components which take advantage of existing location determination systems, these components would substantially increase costs of the subscriber units. Moreover, relying on existing location determination systems could reduce reliability of the radio telecommunications system by introducing reliance upon an external system.
The techniques used by such prior art systems to determine location could potentially be incorporated into the radio telecommunications system, but the introduction of such techniques could seriously degrade communication services. For example, most prior art location systems require the use of two or more transmitters or receivers ("locators") that are located at distant positions and that are capable of transmitting or receiving signals to or from a location to be determined.
The requirement for two or more locators to be within view over the entire globe makes this approach impractical. While this requirement might be met by placing satellites in high or geosynchronous orbits around the earth, higher orbits place satellites further away from subscriber equipment on the earth. This larger distance causes the subscriber equipment to consume excessive power or incorporate massive antennas just to participate in communication services. Moreover, higher orbits require increased spectrum allocation to carry a given amount of communications because the allocated spectrum can be reused less frequently in a given area.
Prior art systems also perform signal source location within a number of pre-defined scenarios. GPS, for example, uses a number of signal time of arrival (TOA) along with current time to determine location. Although this system works well within the predefined scope, the measured quantities must be appropriate for that system. In addition, when all measurements are not available, no solution is possible. Furthermore, additional signal data from other measurements or observations can not be used to enhance the solution. The location of a signal source, such as a subscriber unit is further complicated by real-world environmental problems such noise and atmospheric effects which have an effect on the accuracy of signal measurements, and the resultant location.
Thus what is needed are an improved radio telecommunications system and method. What is also needed are a method and apparatus that determines the location of subscriber units relatively quickly. What is also needed are a method and apparatus that determines the location of a subscriber unit with one or more signal observation. What is also needed are a method and apparatus that uses a variety of received signal data to determine the location of a signal source. What is also needed are a method and apparatus that is flexible enough to adapt to various input to determine the location of a signal source. What is also needed are a method and apparatus that uses either simultaneous signal measurements or signal measurements spaced out in time. What is also needed are a method and apparatus that uses additional observations or measurements of various types to enhance a location solution. What is also needed are a method and apparatus that provides a confidence level for solution locations when exact solutions are not possible.